Cast cylindrical polyvinyl alcohol brushes are conventionally used in automatic cleaning systems to provide a post CMP (Chemical Mechanical Planarization) process to effectively clean surfaces of substrates such as semiconductor wafers or other disc-shaped substrates. Cylindrical polyvinyl alcohol brushes are also used in cleaning systems to clean and dry glass and other non-disc-shaped substrates in flat panel display manufacture, glass production, and printed circuit board assembly. Cylindrical brushes preferably have a length as short as 50 millimeters or as long as 10 meters, for example.
The cylindrical brushes are located on and driven by a central brush mandrel in the cleaning process. An accurate and stable connection between the cylindrical brush and the central brush mandrel is desirable. The cylindrical brushes may have nodules on their outer surface to help clean the substrate.
The cylindrical brushes are expected to accurately rotate on their axis and provide a generally cylindrical surface with a generally consistent nodule pressure pattern over their useful life, which defines optimum cleaning of the entire substrate surface in the least amount of time with minimal damage to the substrate surface.
In some cases, the cylindrical brush is formed around the central brush mandrel. For example, the brush mandrel may be placed in a mold and a mixture of chemicals, such as polyvinyl alcohol, is injected into the mold to form the cylindrical brush around the central brush mandrel. With reference to FIGS. 1A and 1B, in previous brush mandrel designs, a brush mandrel 30 may include a plurality of odd shaped nooks, cracks, and crevices 52 formed on an outer surface 54 of the brush mandrel 30 to better engage and hold the cylindrical brush. As the cylindrical brush 110 is formed around the brush mandrel 30, gas bubbles may get trapped in the crevices 52 and either remain in the crevices 52 or rise and be trapped within the cylindrical brush 110 as the cylindrical brush 110 is forming. The trapped gas bubbles form defects in the cylindrical brush 110 which prevent the cylindrical brush 110 from performing as designed.
Additionally, at times, over the life of the cylindrical brush, there will typically be a tendency for the brush to move axially or rotationally by partially slipping on the brush mandrel and this is regarded as unsatisfactory performance. As a result, it would be desirable to have a brush mandrel which can provide an accurate and stable connection between the cylindrical brush and the central brush mandrel and which can prevent gas bubbles from forming or being trapped in the cylindrical brush.